Simulations based on the standard cosmological model completed in 2011 indicate that galaxies should be uniformly distributed. But the universe appears to be clumpier than astronomers expected, according to the largest galaxy survey ever conducted. The extra clumps could call for a redesign of the standard model of cosmology, and maybe a new understanding of how gravity works. It will be interesting to see if this does bear out, if the standard picture can be changed with a few minor tweaks, or if we need a whole-scale revision.

“Maybe on very large scales, Einstein’s general relativity is slightly wrong,” said cosmologist Shaun Thomas of University College London. “This potentially could be one of the first signs that something peculiar is going on.”

When viewed close up, the matter in the universe bunches up into stars, galaxies and galaxy clusters. But as you zoom out, cosmologists expect the universe to look more and more smooth, sort of the way details in an earthly landscape blend together when viewed from an airplane.

What clumpiness there is comes from tiny fluctuations in the density of matter in the early universe. As the universe expanded, spots with a little bit of extra matter gathered more and more matter through gravitational attraction. Based on the best model of how gravity works and what the universe is made of, cosmologists can extrapolate out from the Big Bang to get a pretty good idea of how lumpy the universe should be on every scale.

Thomas and colleagues looked at the most zoomed-out view of the universe yet acquired, and found more lumpiness than models predict, using data from the Sloan Digital Sky Survey, which covers about a fifth of the entire sky, to make a rough 3-D map of 723,556 galaxies that are at least 4 billion light-years away. The researchers calculated how evenly distributed, or smooth, the galaxies appear on length scales of 2 billion light-years.

“These are scales which are starting to approach a reasonable fraction of the size of the universe, and they haven’t really been measured before,” said ” physicist Michael Hudson of the University of Waterloo in Canada, who was not involved in the work.

The clumpiness of the universe is expected to vary by about 1 percent from one spot to another on these length scales. The new analysis saw a universe that varies by nearly double that amount. It’s still basically smooth, but much clumpier than current cosmological models predict

The result could mean cosmologists need to reassess their understanding of dark energy, the mysterious force that drives the universe outward at an ever-increasing rate. Dark energy itself is supposed to be almost perfectly smooth, but clumps of dark energy could draw clumps of visible matter around them.

The extra lumps could also mean dark energy doesn’t exist at all. Instead, gravity could behave differently on very large scales than it does on smaller scales, meaning Einstein’s theory of general relativity needs an overhaul.

“General relativity has proved right time and time again, but it’s been tested over the same scales,” Thomas said. “These are new scales, so it could be that something breaks down. And then you need some new theory.”

Of course, the clumpiness could also come from systematic errors in the observations, like stars masquerading as galaxies or dust in the Milky Way blocking distant galaxies from view. Thomas and colleagues checked both of these possibilities and think they’re unlikely to be a problem, but there’s still some room for questions.

Bigger and newer data sets, like that offered by the upcoming Dark Energy Survey, are expected help resolve lingering doubts.

The image at the top of the page shows galaxy cluster Abell 383, which is located about 2.3 billion light years from Earth, one of the largest gravitationally-bound structures in the universe.

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Comments

On a small scale, gravity as we know it might ok, just that it might be a first order approximation. Or, at larger distances the universe is seen to be slightly non-flat. Maybe both points of view are equivalent.

Or perhaps is time to wake up from denial no matter how difficult is to contradict the main stream established theory, there was no single big bang and the calculation for distance and speed based on red shift are not accurate(as noticed for NGC7603, NGC4319 and many others) since both speed and distance calculation are based on it but are interrelated.

Perhaps each galaxy or quasar is a individual big-bangs created constantly by large quantum fluctuations. Or perhaps we are to young to understand the origin of the universe, let's not say we know and lie just by being afraid of admitting we don't know yet.

People always forget that these models they build are based on probabilities. There is no rule or law that says the most likely things to happen should and do happen. They are just most likely. In reality, random is unevenly distributed and "fitting the model" would be only one of thousands of possible outcomes.

“These are scales which are starting to approach a reasonable fraction of the size of the universe"
How about "known universe" since there could be another Earth 30 Billion Light-Years away and they couldn't see the same galaxies we see because the light range spheres haven't touched.

I think Dark Matter and Dark Energy currently still are such enigma's that a rework of our understanding of these factors aren't ruled out at all. These simulations will only help in creating a new and better understanding of these "Dark factors" and finally revealing what they really entail. This simulation just proves that we're not there yet.

Perhaps the error is the notion that the Universe is electrically neutral – that electricity does not “do anything” in space. It is a perverse stance given the overwhelming importance of electricity in our lives.

Gravitation theory proved to be wrong when it was unable to explain large scale structures in the universe. Dark energy and dark matter are only desperates attempts to maintain alive something that sooner or later must be completely rethought.

If Einstien could be around today with all of these discoveries and what not, I think he himself would re-think his theory of relativity.
He made his theory based on observations and what was known at the time, just like all the ones before him that were proven wrong as science progressed.

@Greg,
Yes, just think of what is discovered since Newton, the scientific dinosaur, who still are ruling the modern cosmology.

"Gravity" the most unknown and illusive "force" demands a huge amount of "added epicycles" in order to survive as a theory on the big scale.

But even Einsteins "curvature of space" is far out of any logical order.

Space doesn´t have such quality in itself, but everything IN the space moves in curves or swirls, namely thermodynamical and electromagnetic swirls and circuits, and this goes for a single atom to superclusters and so on.

There's so much peculiar going on in the universe, and this was the researchers' first clue?

Quantum theory shows that events are based on possibility; a favorite saying of physicists is that whatever is not forbidden is required. In other words, if it can happen, it will happen.

Cosmologists explaining the "universal waveform" (the set of probabilities for the events in the universe coming to a particular result) have generally put our own existence at or near the top of the probability waveform. But that's not necessarily the case. Most likely we're off to the side, about halfway up.

It may well be that this somewhat-unlikely clumping at cosmological scales is, in the long term, necessary for life to form and continue. Thus, while the uniform distribution of matter may be the most likely probability, we'd never be able to observe it unless we can figure out a way to travel "sideways" in time to that higher-probability timeline.

Yes, this is purely a layman's conjecture. But consider: the best place in the solar system to be is not too close to the sun, nor too far. The best place in the galaxy to be is not too close to the core, nor too far. Not too hot, or too cold; not too heavy, or too light -- those may not be the only "Goldilocks zones" we need.